1,3-disulfonylcycloalkane

ABSTRACT

1,3-Disulfonylcycloalkanes substituted in the 2-position with at least one hydrogen atom are employed as silver halide complexing agents in both conventional and diffusion transfer photography. Preferred compounds are those possessing an S-containing moiety substituted in the 2-position and particularly those containing 6, 7 or 8 members in the cyclic ring and substituted in the 2-position with R 2  -S--CH 2m  wherein R 2  is a hydrocarbon radical and m is a whole number 0 to 5. The latter thioether-substituted 1,3-disulfonylcycloalkanes comprise the novel compounds of the present invention.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This application is a division of U.S. application Ser. No. 535,205filed Dec. 23, 1974, now U.S. Pat. No. 3,958,992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to photography and, in particular, it isconcerned with a new class of silver halide solvents and withphotographic products, processes and compositions employing the same.

2. Description of the Prior Art

Photographic processing compositions capable of forming water-solublecomplex silver salts are known to be useful in many types of silverhalide photography. To obtain a relatively stable image in an exposedand developed photosensitive silver halide emulsion, the silver halideremaining in the unexposed and undeveloped areas of the emulsion shouldbe converted to a soluble silver complex that can be removed by washingor converted to a stable silver complex that will not "print-out" uponprolonged exposure to light. In conventional or "tray" development, itis customary to fix the developed silver halide emulsion by applying asolution of silver halide solvent, i.e., silver halide complexing agentwhich forms a water-soluble silver complex with the residual silverhalide. The water-soluble silver complex thus formed and excess silverhalide solvent are then removed from the developed and fixed emulsion bywashing with water.

Silver halide solvents also have been employed in monobaths where asingle processing composition containing a silver halide developingagent in addition to the silver halide solvent is utilized for bothdeveloping and fixing an exposed photosensitive silver halide layer.Silver halide solvents also have been employed in diffusion transferphotographic processes. Such processes are now well known in the art;see for example, U.S. Pat. Nos. 2,543,181; 2,647,056; 2,983,606; etc. Inprocesses of this type, an exposed silver halide emulsion is treatedwith a processing composition whereby the exposed silver halide emulsionis developed and an imagewise distribution of diffusible image-formingcomponents is formed in the unexposed and undeveloped portions of thesilver halide emulsion. This distribution of image-forming components istransferred by imbibition to an image-receiving stratum in superposedrelationship with the silver halide emulsion to provide the desiredtransfer image. In diffusion transfer processes where a silver transferimage is formed, processing is effected in the presence of a silverhalide solvent which forms a diffusible complex with the undevelopedsilver halide. The soluble silver complex thus formed diffuses to thesuperposed image-receiving layer where the transferred silver ions aredeposited as metallic silver to provide the silver transfer image. Inpreparing silver prints in this manner, the image-receiving elementpreferably includes a silver precipitating agent, for example, heavymetal sulfides and selenides as described in U.S. Pat. No. 2,698,237 ofEdwin H. Land.

Various compounds have been employed as silver halide solvents in thephotographic processes described above. One of the most commonlyemployed is sodium thiosulfate. Other silver halide solvents that havebeen used include thiocyanates, such as potassium and sodiumthiocyanate; mercaptans, such as mercaptoacetic acid and cysteine;alkali metal cyanides, such as potassium cyanide; and cyclic imides,such as barbituric acid and uracil. U.S. Pat. No. 3,769,014 disclosesstill another class of silver halide solvents, namely, β-disulfones butis limited to the use of open-chain compounds, i.e., 1,1-bis-sulfonylalkanes though various cyclic β-disulfones are known per se in the art.

According to the present invention, it has been found that certaincyclic β-disulfones are also useful as silver halide solvents.

SUMMARY OF THE INVENTION

It is, therefore, the primary object of the present invention to providephotographic products, processes and compositions employing certaincyclic β-disulfone silver halide solvents.

It is another object of this invention to provide novel β-disulfonesuseful as photographic silver halide solvents.

Other objects of this invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the processes involving the severalsteps and the relation and order of one or more of such steps withrespect to each of the others, and the products and compositionspossessing the features, properties and the relation of elements whichare exemplified in the following detailed disclosure, and the scope ofthe application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, it has now been found that cyclic β-disulfones areuseful for complexing silver ion, i.e., undeveloped silver halide inphotographic processes. Cyclic β-disulfones found particularly useful inboth conventional and diffusion transfer photography are1,3-disulfonylcycloalkanes, i.e., cyclic alkanes with two intralinear--SO₂ -- groups positioned β to each other, which possess 6, 7 or 8members in the cyclic ring (including said sulfonyl groups) and whereinthe 2-carbon atom is substituted with at least one hydrogen atom.Particularly useful compounds of this type are those represented in thefollowing formula: ##STR1## wherein R is hydrogen or a monovalentorganic radical and n is a whole number 3, 4 or 5.

As used herein, "monovalent organic radical" is intended to include bothcyclic and acyclic organic radicals whether homogeneous or heterogeneousin nature. Typical radicals useful as the R moiety are alkyl,substituted and unsubstituted; alkyl wherein the carbon chain isinterrupted with a heteroatom, substituted and unsubstituted;cycloalkyl, substituted and unsubstituted; alkenyl, substituted andunsubstituted; cycloalkenyl, substituted and unsubstituted; and aryl,substituted and unsubstituted. Generally, the substituents of thesubstituted monovalent organic radicals are solubilizing groups, i.e.,groups selected to make the compound soluble in the particular liquidvehicle used. Typical of such substituents are --SO₃ H, --OH, --NH₂ and--COOH, particularly where the liquid vehicle is aqueous. Among othersubstituents that may be present, if desired, are halo, nitro, cyano,and alkoxy.

In the above-described 1,3-disulfonylcycloalkanes, the proton (hydrogen)on the carbon atom in the 2-position is removable in alkali to providethe corresponding C.sup.⊖ anion. In a preferred embodiment, the Rsubstituent is a moiety containing --S--, excluding --SH and moietiesthat would form --SH in alkali, wherein said sulfur atom of said moietyis positioned adjacent to or up to 6 or 7 atoms away from said carbonatom. The --S-- containing moiety preferably is R'S--(X)_(m) -- whereinR' is a monovalent organic radical, usually a hydrocarbon radical, whichmay be unsubstituted or substituted with e.g., a solubilizing group orgroups; X represents a carbon atom, a heteroatom or a mixture of carbonatoms and heteroatoms and m is a whole number 0 to 5. The --S-- of saidR'S--(X)_(m) -- moiety should be in a position alpha, beta, gamma,delta, epsilon or zeta to the C.sup.⊖ anion as illustrated below whereinY represents the residue of the 1,3-disulfonylcycloalkane:

Y--c.sup.⊖ --sr'; alpha

Y--c.sup.⊖ --x--sr'; beta

Y--c.sup.⊖ --x--x--sr'; gamma

Y--c.sup.⊖ --x--x--x--sr'; delta

Y--c.sup.⊖ --x--x--x--x--sr'; epsilon

Y--c.sup.⊖ --x--x--x--x--x--sr'; zeta

Preferably, the position of --S-- with respect to the C.sup.⊖ anion isalpha, gamma, delta, epsilon or zeta.

The compounds substituted with an --S-- containing moiety as describedabove comprise per se novel compound within the present invention. In aparticularly preferred embodiment, the subject compounds have theformula: ##STR2## wherein R¹ is R² --S--CH₂ --_(m) wherein R² is ahydrocarbon radical containing up to about 20 carbon atoms selected fromalkyl, aryl, alkaryl and aralkyl, said hydrocarbon radical beingunsubstituted or substituted with a solubilizing group selected fromcarboxy, sulfo, hydroxy and amino, m is a whole number 0, 1, 2, 3, 4 or5 and n is a whole number 3, 4 or 5. Preferably, R² is lower alkylcontaining 1 to 4 carbon atoms, unsubstituted or substituted with asolubilizing group and n is 3 or 4.

Illustrative R² groups include alkyl, such as, methyl, ethyl, propyl,isopropyl, n-butyl, t-butyl, hexyl, octyl, dodecyl, hexadecyl andoctadecyl; aryl, such as phenyl and naphthyl; alkaryl, such asp-hexylphenyl, p-octylphenyl and p-dodecylphenyl; and aralkyl, such asbenzyl, phenethyl and phenylhexyl. As mentioned above, to enhance thesolubility of the compound in aqueous alkaline solution, the R² groupmay be substituted with a solubilizing group(s), such as thoseenumerated above. Preferred substituted R² groups are w-R³ -alkyl, w-R³-alkaryl, p-R³ -aryl and p-R³ -aralkyl wherein R³ is carboxy, hydroxy,sulfo or amino, i.e., --NR₁ R₂ wherein R₁ and R₂ each are selected fromhydrogen and alkyl, preferably lower alkyl containing 1 to 4 carbonatoms.

Specific examples of compounds useful as silver halide solvents inaccordance with the present invention are those set out in the followingformulas. It will be appreciated that those compounds substituted withan --S-- containing moiety as described above illustrate the per senovel compounds of the present invention. ##STR3##

The non-S-substituted 1,3-disulfonylcycloalkanes may be synthesized in aconventional manner from the corresponding 1,3-dithiocycloalkanes, suchas, 1,3-dithiane and 1,3-dithiepane as described, for example, in Ber.,32, p. 1375 (1899) and Tetrahedron Letters, 1962, p. 515. The compoundssubstituted with the --S-- containing moiety may be prepared, forexample, by reacting the 1,3-disulfonylcycloalkane with thechlorosubstituted derivative of the selected R¹ substituent, i.e., R²--S--(CH₂)_(m) --Cl as described in the following examples which areintended to be illustrative only.

EXAMPLE I

Preparation of the compound of formula (2):

In a 3-neck round bottom flask fitted with thermometer, dropping funneland air condenser, 1,3-dithiane (20 g., 0.166 mole) was dissolved in 100ml. glacial acetic acid. A solution of commercial 40% peracetic acid(139 g., about 0.73 mole) was diluted with 100 ml. glacial acetic acidand was added dropwise over 1 hour and the temperature maintained atabout 70° C. A large amount of white solid crystallized from thereaction mixture. After heating for an additional one hour at 60°-70°C., the solid was collected, pressed dry, slurried with water,collected, and pressed dry. Final drying was effected by washing with asmall volume of cold methanol followed by ether to give 28.7 g. (94% byweight) of 1,3-dithiane disulfone (1,3-dithiane-1,1,3,3-tetraoxide), thecompound of formula 1.

In a dry 3-neck round bottom flask fitted with a dropping funnel,thermometer, air condenser with nitrogen inlet and magnetic stirrer,1,3-dithiane disulfone (6.7 g., 36.4 mmoles) was suspended in 80 ml. ofN,N-dimethylformamide. Sodium hydride (57% mineral oil dispersion, 1.53g., 36.4 mmoles) was added in portions. The reaction mixture was stirredat 40° C. for 1 hour to give a gray solution. A solution ofmethylthiotosylate (7.36 g., 36.4 mmoles) in 10 ml. dimethylformamidewas added dropwise. A voluminous precipitate formed. The reactionmixture was heated to 80° C. and maintained for 3 hours to obtain anearly homogeneous reaction mixture. The resulting homogeneous mixturewas allowed to cool and then poured onto ice containing 4 ml.concentrated hydrochloric acid. The off-white solid was collected andair-dried (approximately 8 g., melting range 271°-5° C.). The crudeproduct was recrystallized from hot N,N-dimethylformamide (1 g./3 ml.)and clarified with Norit to give 2.6 g. (31% by weight) of the titlecompound, melting range 280°-282° C. A second crop of the title compound(2.3 g., 28% by weight) was obtained by diluting with an equal volume ofwater.

    ______________________________________                                                      C          H                                                    ______________________________________                                        Theory          26.05        4.35                                             Found           26.4         4.40                                             ______________________________________                                    

EXAMPLE II

Preparation of the compound of formula (3):

A warm slurry of 1,3-dithiane disulfone (18.4 g., 100 mmoles) inapproximately 200 mls. of N,N-dimethylformamide was added to a slurry ofsodium hydride (57% mineral oil dispersion, 42. g., 100 mmoles) inapproximately 30 mls. of N,N-dimethylformamide. This mixture was stirredfor about one-half hour at 50°-60° C. to give a clear gray solution.2-chloroethylmethylsulfide was added dropwise to the solution over 15minutes and stirring was continued at 50°-60° C. overnight. Theresulting yellow-brown solution (some white granular solid separated)was poured into 1 liter of ice water containing 10 mls. of concentratedhydrochloric acid to give a gray solid. The gray solid was trituratedwith ether, and 5 g. of the crude product was recrystallized from 125mls. of hot ethanol to give 2.3 g. of the title compound as a whitesolid (melting point 157° C.).

    ______________________________________                                                  C        H          S                                               ______________________________________                                        Theory      32.6       5.43       37.2                                        Found       32.6       5.38       37.45                                       ______________________________________                                    

EXAMPLE III

Preparation of the compound of formula (4):

1,3-dithiane disulfone (2.5 g., 13.6 mmoles) and sodium hydride (57%mineral oil dispersion, 0.57 g., 13.6 mmoles) were stirred together in30 mls. of N,N-dimethylformamide for about 2 hours at a temperature ofabout 35° C. under nitrogen. 3-chloropropylmethylsulfide (1.7 g., 13.6mmoles) was added, and the reaction mixture was stirred at about 65° C.overnight. The formation of solid was noticeable after about one-halfhour. The reaction mixture was poured onto ice concentrated hydrochloricacid (3 ml.). The white solid was collected and triturated withpetroleum ether. Recrystallization from 100 mls. of hot ethanol gave 2g. of the title compound as a white solid (melting range 133°-136° C.).

EXAMPLE IV

Preparation of the compound of formula (5):

Sodium hydride (57% mineral oil dispersion, 1.35 g., 32.8 mmoles) wasadded in one portion to a suspension of 1,3-dithiane disulfone in 35mls. of N,N-dimethylformamide, and the mixture was stirred about 45minutes at 40°-50° C. to give a gray solution.S-(2-chloroethyl)-ethylmercaptoacetate (6 g., 32.8 mmoles) in 15 mls. ofN,N-dimethylformamide was added dropwise to the solution over 15 minuteswith stirring and stirring was continued at room temperature overnight.The reaction mixture was then poured onto ice concentrated hydrochloricacid (3 ml.). A taffy separated which soon solidified on scratching.This solid was collected, washed well with water and triturated withpetroleum ether. Of the 7.3 g. of solid collected, approximately 5 g.was recrystallized from 100 mls. of methanol. About 0.9 g. of insolubleswas discarded, and about 2.0 g. of the ester intermediate was recoveredas white needles (melting range 126°-128° C.).

Hydrochloric acid (4 mls. of approximately 3 N acid) was added to asuspension of the ester prepared above in 10 mls. ethanol. The mixturewas heated to reflux, and a solution was obtained in about 10 minutes.Heating was continued for about 3 hours. The solution was then allowedto cool and stand overnight. The white crystalline material that formedwas collected and discarded, and 4 mls. of approximately 5 Nhydrochloric acid was added to the solution. After heating at reflux for6 hours, 10 mls. of water was added and heating at reflux was continuedovernight. The solution was cooled and the ethanol stripped leaving awhite crystalline solid. 10 mls. of 6 N hydrochloric acid was added tothe crystalline material. The resulting solution was heated at refluxfor about 4 hours and then stripped to give a solid which was trituratedwith ether and collected (about 1.0 g.). The solid was taken up in about13 mls. of hot water, the solution quickly cooled to room temperature,filtered and allowed to stand at room temperature for 2 days. The titlecompound was then recovered as white clusters (melting range 151°-152°C.).

EXAMPLE V

preparation of the compound of formula (9):

A sample of partially purified 1,3-dithiepane [prepared according toTetrahedron, 20, 427 (1964)] (1.5 g., about 10 mmoles) was dissolved inglacial acetic acid, and 40% peracetic acid (10 g., about 50 mmoles) wasadded slowly dropwise. The reaction was allowed to stir overnight atroom temperature when the white solid precipitate was collected andwashed with water to give approximately 50% crude product (melting range175°-178° C.) which was homogeneous by TLC. Recrystallization from hotwater afforded the title compound, 1,3-dithiepane-1,1,3,3-tetraoxide, aswhite needles (melting range 190°-192° C.)

In formulating photographic processing compositions utilizing theabove-described compounds, the compounds may be used singly or inadmixture with each other. The total amount employed may vary widelydepending upon the particular photographic system and should be used,for example, in a quantity sufficient for fixing a developed negative inconventional "tray" processing or in a quantity sufficient to give asatisfactory transfer print in diffusion transfer processes under theparticular processing conditions employed.

Though the silver halide solvents of the present invention are broadlyuseful in a variety of photographic processes of the type in whichwater-soluble silver complexes are formed from the unreduced silverhalide of a photoexposed and at least partially developed silver halidestratum, they find particular utility in diffusion transfer processes. Acomposition embodying the present invention specifically suitable foruse in the production of transfer images comprises, in addition to thesilver halide complexing agents of the above-described type, a suitablesilver halide developing agent, preferably an organic developing agent.Examples of developing agents that may be employed include hydroquinoneand substituted hydroquinones, such as tertiary butyl hydroquinone,2,5-dimethyl hydroquinone, methoxyhydroquinone, ethoxyhydroquinone,chlorohydroquinone; pyrogallol and catechols, such as catechol, 4-phenylcatechol and tertiary butyl catechol; aminophenols, such as2,4,6-diamino-orthocresol; 1,4-diaminobenzenes, such asp-phenylenediamine, 1,2,4-triaminobenzene and4-amino-2-methyl-N,N-diethylaniline; ascorbic acid and its derivatives,such as ascorbic acid, isoascorbic acid and 5,6-isopropylidene ascorbicacid and other enediols, such as tetramethyl reductic acid; andhydroxylamines, such as N,N-di-(2-ethoxyethyl)hydroxylamine andN,N-di-(2-methoxyethoxyethyl)hydroxylamine.

In diffusion transfer processes, the processing composition, if it is tobe applied to the emulsion by being spread thereon in a thin layer, alsousually includes a viscosity-imparting reagent. The processingcomposition may comprise, for example, one or more silver halidesolvents of the present invention, one or more conventional developingagents such as those enumerated above, an alkali such as sodiumhydroxide or potassium hydroxide and a viscosity-imparting reagent suchas a high molecular weight polymer, e.g., sodium carboxymethyl celluloseor hydroxyethyl cellulose.

In one such transfer process, the processing solution is applied in auniformly thin layer between the superposed surfaces of a photoexposedphotosensitive element and an image-receiving element, for example, byadvancing the elements between a pair of pressure-applying rollers. Theelements are maintained in superposed relation for a predeterminedperiod, preferably for a duration of 15 to 120 seconds, during whichexposed silver halide is reduced to silver and unreduced silver halideforms a water-soluble, complex salt which diffuses through the layer ofsolution to the image-receiving element, there to be reduced to anargental image. At the end of this period, the silver halide element isseparated from the image-receiving element. Materials useful in such atransfer process are described in U.S. Pat. No. 2,543,181, issued in thename of Edwin H. Land on Feb. 27, 1951, and in numerous other patents.

The photosensitive element may be any of those conventionally used insilver diffusion transfer processes and generally comprises a silverhalide emulsion carried on a base, e.g., glass, paper or plastic film.The silver halide may be a silver chloride, iodide, bromide,iodobromide, chlorobromide, etc. The binder for the halide, thoughusually gelatin, may be a suitable polymer such as polyvinyl alcohol,polyvinyl pyrrolidone and their copolymers.

The image-receiving element preferably includes certain materials, thepresence of which, during the transfer process has a desirable effect onthe amount and character of silver precipitated on the image-receivingelement. Materials of this type are specifically described in U.S. Pat.Nos. 2,690,237 and 2,698,245, both issued in the name of Edwin H. Landon Dec. 28, 1954.

Separating of the silver halide element from the image-receiving elementmay be controlled so that the layer of processing composition is removedfrom the image-receiving element or the layer of processing compositionis caused to remain in contact with the image-receiving element, e.g.,to provide it with a protective coating. Techniques which enable suchresults to be accomplished as desired are described in U.S. Pat. No.2,647,054 issued to Edwin H. Land on July 28, 1953. In general, theprocessing reagents are selected so that traces remaining after thesolidified processing layer has been separated from the silver image orwhich remain in said layer adhered as a protective coating on the silverimage, as indicated above, are colorless or pale, so as not toappreciably affect the appearance of the image and to have little or notendency to adversely react with the silver image.

The silver halide solvents of the present invention also may be employedin diffusion transfer processes adapted to provide positive silvertransfer images which may be viewed as positive transparencies withoutbeing separated from the developed negative silver image including suchprocesses adapted for use in forming additive color projection positiveimages. Diffusion transfer processes of this type are described in U.S.Pat. Nos. 3,536,488 of Edwin H. Land and 3,615,428 of Lucretia J. Weedand in U.S. application Ser. No. 383,196 of Edwin H. Land filed July 27,1973, now U.S. Pat. No. 3,894,871. The subject compounds also findutility as silver halide solvents in diffusion transfer processesutilizing the properties of the imagewise distribution of silver ions inthe soluble silver complex made available in the undeveloped andpartially developed areas of a silver halide emulsion to liberate areagent, e.g., a dye in an imagewise fashion, as described in U.S. Pat.No. 3,719,489 of Ronald F. W. Cieciuch, Roberta R. Luhowy, Frank A.Meneghini and Howard G. Rogers.

The following example is given to illustrate the utility of thecompounds of the present invention as photographic silver halidesolvents and is not intended to be limiting.

EXAMPLE VI

A negative comprising a photosensitive silver halide emulsion wasexposed to a step wedge and processed by spreading a layer of processingcomposition approximately 1.2 mils. thick between the exposed emulsionand a superposed image-receiving element comprising a layer ofregenerated cellulose containing colloidal palladium sulfide carried ona transparent support. The processing composition was prepared by addinga silver solvent of the present invention in a concentration of 5% byweight to the following formulation:

    ______________________________________                                        Water                    814.0     g.                                         Potassium hydroxide                                                           (Aqueous 50% w/w solution)                                                                             348.0     g.                                         Hydroxyethyl cellulose   35.0      g.                                         Zinc acetate             15.0      g.                                         Triethanolamine          5.6       g.                                         Bis-N,N-methoxyethyl                                                          hydroxylamine            50.0      g.                                         ______________________________________                                    

After an imbibition period of approximately one minute, the negative wasseparated from the image-receiving element, and the maximum and minimumtransmission densities were measured for the positive image.

The compounds added to the base formulation as silver halide solvents,and the density measurements for the positive image obtained with eachof the compounds are set forth in the following table:

                  TABLE                                                           ______________________________________                                        Compound         Density                                                      (Formula No.)    Maximum     Minimum                                          ______________________________________                                        (1)              1.60        0.40                                             (2)              0.95        0.08                                             (5)              1.20        0.10                                             (9)              2.60        0.80                                             ______________________________________                                    

In a visual comparison of the negative images obtained with thecompounds listed in the above table, it was observed that the compoundssubstituted with the --S-- containing moiety gave enhanced negativefixing, i.e., lower background. Also, it was observed that a substantialincrease in positive speed, approximately 4 to 5 stops, was obtainedwith these substituted compounds.

It will be apparent that the relative proportions of the subject silverhalide solvents and of the other ingredients of the processingcompositions may be varied to suit the requirements of a givenphotographic system. Also, it is within the scope of this invention tomodify the formulations set forth above by the substitution of alkalies,antifoggants and so forth other than those specifically mentioned. Wheredesirable, it is also contemplated to include in the processingcompositions, other components as commonly used in the photographic art.

Since certain changes may be made in the above compositions andprocesses without departing from the scope of the invention hereininvolved, it is intended that all matter contained in the abovedescription should be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. A compound of the formula ##STR4## wherein R² isa hydrocarbon radical containing up to 20 carbon atoms selected fromalkyl, aryl, alkaryl and aralkyl, said hydrocarbon radical beingunsubstituted or substituted with a solubilizing group selected from--COOH, --SO₃ H, --OH and --NR₁ R₂ wherein R₁ and R₂ each is selectedfrom hydrogen and lower alkyl containing 1 to 4 carbon atoms, m is awhole number 0, 1, 2, 3, 4 or 5 and n is a whole number 3, 4 or
 5. 2. Acompound as defined in claim 1 wherein said solubilizing group is--COOH.
 3. A compound as defined in claim 1 wherein said R² is alkyl. 4.A compound as defined in claim 3 wherein n is
 3. 5. A compound asdefined in claim 3 wherein n is
 4. 6. The compound ##STR5##
 7. Thecompound ##STR6##
 8. The compound ##STR7##
 9. The compound ##STR8##